Strategy for predicting transport-based durability properties of concrete based on DEM approach

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Strategy for predicting

transport-based durability properties of

concrete based on DEM approach

Kai Li, L.B.N. Le, Piet Stroeven, Martijn Stroeven Civil Engineering and Geosciences Faculty,

Delft University of Technology, the Netherlands

RILEM international workshop on performance-based specification and control of concrete durability, Zagreb, Croatia, 11 – 13 June, 2014

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Outline

• Transport-based durability issues of concrete

• Discrete element method (DEM)

• Pore network characteristics of hydrated paste

• Simulation of hydrated structure on nano-scale

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Transport-based durability issues of concrete

Durability problems of concrete Fluid, ion transport in concrete

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Transport-based durability issues of concrete Three types of pores in cement-based materials:

•Gel pores few nanometers

•Capillary pores 1 nm – 10 µm

•Macro-pores (air voids) lager than 10 µm

Jing Hu, PhD thesis, Delft, 2004

Available techniques for pore exploration: • MIP (Mercury Intrusion Porosimetry) • IA (Images Analysis)

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Transport-based durability issues of concrete

Macroscale Mesoscale Microscale Nanoscale

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Discrete element method (DEM)

Newtonian system with particles (HADES package)

Linear direction: i i ij i j v F f m t    

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Angular direction: i i ij i j M m I t    

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Pore network characteristics of hydrated paste

HADES: dynamic DEM for packing simulation of fresh cement grains (Rosin-Rammler distribution).

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XIPKM: extended integrated particle kinetics method for simulation of fresh multi-component cement system.

r_o r_o rout t = 0 t > 0 C3S C2S SiO2 CSH-in CSH-out CH Inert a in r b in r b  a  r_o ro rout a  a in r

(left) particle model for multi-component cement grain

(right) differently color-coded microstructure of hydrated paste

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DRaMuTS: double random multiple tree structuring system for delineating the complete pore network system and for

topology assessment.

Different colors is for trees from different seeds

The main trunks in continuous pore channels Illustration of DRaMuTS

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points in percolated pores points in isolated pores

points in main channels points in dead-end pores

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SVM: star volume measurements in uniformly random point system inside the pore network

Pore size distribution in 1-30 m fully hydrated PC with w/c=0.3

C1: 6P C2: 4P+2R

P: periodic boundaries R: rigid boundaries

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Validation

Hydration curves of PC (left) and porosity curves of RHA-blended PC samples for prolonged hydration (right). Note that 40/25 means wc=0.4/0.25; 10/20 % PC blending.

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Simulation of hydrated structure on nano-scale However, “overestimation” of pore size distribution does exist……

Besides, for investigating transport-based durability properties of cementitious materials, surface roughness of hydration

product needs to be taken into account……

If we move from micro-level to nano-scale, probably solutions to our problems can be found……

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Simulation of hydrated structure on nano-scale

HD C-S-H LD C-S-H

C₃S

Assumed boundaries between HD and LD C-S-H

LD C-S-H HD

C-S-H

I.G. Richardson, Cement and Concrete Research, 34 (2004) 1733-1777

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• C-S-H (calcium silicate hydrate), the main hydration product, important but complex gel.

• Granular nature and fractal dimension of C-S-H is suggested by Jennings’ colloidal model, meanwhile, fibrous morphology is revealed by experimental techniques.

• New mechanism should be employed based on existing Information to produce more realistic product.

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2D illustration of hydrated structure on nano-scale a) b) c) d) a: stage 1 b: stage 2 c: stage 3 d: stage 4

red: cement grain blue: outer C-S-H white: pore space

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Structural analysis – pore size distribution

S. Diamond, Cement and

Concrete Research, 30 (2000) 1517-1525

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Conclusions

• Micro-level porosimetry approaches are useful for durability estimation purposes.

• The full range of cement particles should be involved for estimating transport properties.

• The nano-level approach could provide more realistic structure and morphology product, compared to the classical vector approach.

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Conclusions

• A realistic shape factor should be added to the resulting expressions.

• A multi-scale techniques should be developed to bridge the gap between micro- and nano-level.

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